This invention relates generally to containers and lids having tamper evident and tamper resistant closures and seals, and particularly to a resealable container closure for use with cylindrical plastic containers of the type in which perishable commodities are packaged.
Plastic containers, pails, tubs, and buckets having various resealable lids with tamper evident or tamper resistant closures are well known to the art. These pails and containers are generally filled with a particular foodstuff or other commodity by an automated container filling machine, and are then sealed and distributed to stores for purchase by the end user. The lid closures are designed such that the containers may not be opened or the contents accessed without revealing visible signs that the seals have been broken. In addition, the closures may include features or elements which make opening the closures or compromising the seals more difficult. Many of the containers and pails may be repeatedly resealed and reused by the purchaser for other applications, although the resealable closures are generally neither tamper evident or tamper resistant, nor provide air tight or moisture proof seals of the degree obtained by the initial sealing processes.
These larger containers, pails, tubs, and buckets may be distinguished from other receptacles, bottles, or jars which include tamper evident closures. The subject containers, pails, tubs, and buckets generally have thin, highly flexible side walls with lids which are snapped on or form a pressure fit. The side walls of the latter bottles and jars are generally rigid with narrow necks, and utilize caps which must be threaded or otherwise rotated onto the neck, or which contain one of several directional locking mechanisms.
One development common to several tamper evident closures is an annular skirt portion which depends from the lower peripheral edge of the lid, and which defines a weakened score line forming a tear strip along the bottom of the skirt. The tear strip will generally have an undercut region which engages an annular ridge which projects radially outward from the outer surface of the container wall, or be positioned such that the distal edge of the skirt is adjacent to or in close confronting contact with a similarly projecting shoulder, and which is torn free from the lid by the user when the original seal is broken.
U.S. Pat. No. 3,510,021 discloses a tear strip and gripping tab configuration in combination with a rigid side wall container having a narrow neck and a cooperating lug and recess arrangement which forms a twist-lock feature, and wherein the score line forming the tear strip is positioned on the outside of the skirt above the upper or most closely adjacent projecting rib. The lid is of the single wall configuration, and the outer side wall of the container presents two ribs. Such a container construction is distinct from the larger pails, buckets, and tubs in which the top or skirt portion of the lid forms a "snap-on" or interference fit seal with a corresponding bead on the container wall.
U.S. Pat. No. 3,672,528 similarly discloses a wide mouth jar and closure in which the score line forming the tear strip is positioned on the outer surface of the skirt above the nearest rib, and wherein the lower distal edge of the skirt is exposed rather than being positioned adjacent to or closely confronting a shoulder. The '528 patent again shows a two rib configuration. However, the lid presents a double wall construction which forms a pressure or friction fit seal with the top rim of the container.
U.S. Pat. No. 3,753,511 discloses a container with a push-in cover having a double walled lid which forms a pressure or compression fit seal with the container rim, and which further defines a bulged portion which increases the clamping force on the container rim which enhances the original seal and the ability to tightly reseal the container. The '511 patent positions the score line defining the tear strip on the outer surface of the skirt, and employs a single rib with no shoulder below the distal edge of the skirt.
U.S. Pat. No. 3,979,003 discloses a container and cover in which the distal end of the skirt portion is closely confronting a shoulder which projects radially outward beyond the outer surface of the skirt, and in which the score line defining the tear strip is positioned along the inner surface of the skirt portion. The '003 patent utilizes a single shoulder, and a single wall cover which is stretched to fit over and engage the top surface of the rim and outer and lower surfaces of a bead on the rim, thereby forming a compression fit which clamps the bead from several directions and creating an entire region of interference fit extending around the surface of the bead.
U.S. Pat. No. 4,037,748 discloses a container and snap-on closure, but wherein the double wall construction of the lid forms three distinct zones of interference fit against both the inner and outer surfaces of the container rim. The '748 patent positions the score line defining the tear strip along the inner surface of the skirt portion, and places the distal end of the skirt closely confronting a shoulder. The '748 patent also discloses an inwardly facing ridge on the inner surface of the skirt portion which rides over and under a sidewall ridge on the outer surface of the container wall when the lid is mounted on the container rim, and which separates the score line from the sidewall ridge.
U.S. Pat. No. 4,667,838 discloses a threaded cap for a rigid walled, narrow mouth bottle with a variation on the traditional double wall lid configuration. The closure shown in the '838 patent has three sealing projections on the outer surface of the container wall, the lowest being a very wide band having a flat outer surface which underlies the skirt portion adjacent to the score line defining the tear strip, and extending a significant distance above and below the score line. In this case, the tear strip is attached to the skirt portion by a plurality of separate connectors, and the skirt portion defines a ring which is permanently engaged under the band such that unthreading the cap from the rim will break the connectors and remove the tear strip from the skirt portion.
U.S. Pat. No. 4,669,623 discloses a single wall cap and narrow necked bottle having threads forming four outward projecting ridges on the container wall, and wherein a score line defining the tear strip is positioned on the outer surface of the skirt portion and adjacent to the third projecting ridge. The tear strip is thus locked between the third and fourth projections, and is torn from the skirt portion when the cap is unthreaded from the rim.
While the above referenced patents disclose a wide variety of containers and lids, each of which combines several different features to form distinct closure structures, these structures do present several recurring problems and defects.
Several of the closure structures are suitable for containers having rigid walls, narrow necks, threaded caps, or for use where a compression or pressure fit seal is desired. However, in many larger containers made of highly flexible thin walled plastic, such as ice cream pails or margarine tubs, these closures would not be suitable or effective.
Of those commodity containers having snap-on lids and tear strips, the tear strip and protective shoulder are generally treated as features which are separate and distinct from, and are therefore not interrelated with, the sealing and closure structure. Consequently, each feature is not utilized to its greatest potential, the sealing structure not cooperating with or enhancing the tamper evidencing features, and the tamper resistance features similarly not cooperating with the sealing features.